Commentaries of the Four Authorized Vaisnava Sampradayas

The question may be raised regarding what type of person is the mind a
friend and to what type of person is the mind an enemy. Lord Krishna
answers that the living being who by spiritual intelligence and diligent
effort has conquered and brought under control the aggregate of the
physical body, the senses and the mind; to this being only can the mind be
considered a friend as a person following an uncontrolled mind is adverse
to their own best interests and is harmful hence their mind is like an
enemy.

Brahma Vaisnava Sampradaya:

Madhvacarya

Madhvacarya's Commentary

To whom is the mind a dear friend has been mentioned by Lord Krishna in
this verse. Here the word atma should be understood as being the mind and
the word atmana as being the living entity. So the meaning is that the
atmana or living entity achieves success by the strength of the atma or
mind. In the Brahmavaivartaka Purana states: That the condition of the mind
is the sole reason for human beings to be liberated from the material
existence or contrarily incarcerated in the material existence. The mind
should elevate a human being and not be a source of delusion and distress
for the mind has the propensity to be the best friend or the worst enemy of
this there is no doubt. When with diligence and determination the mind is
well governed it is like a best friend and then there are no other enemies.
Therefore one should amiably govern their mind by Vedic knowledge and with
devotion to the Supreme Lord. The word atmana refers to one whose mind is
fixed and unconquerable. But even so if the mind is not directed towards
devotion to the Supreme Lord it is not likely to be helpful in the same way
as having a servant who does no work is like not having a servant at all
and soon the mind will become antagonistic to restraint and then an enemy.

Now begins the summation.

The individual consciousness elevates itself by the mercy of the ultimate
consciousness. Lord Krishna is perpetually the best friend and well-wisher
of the righteous and spiritual beings but a perpetual enemy to the
perpetrators of evil and unrighteousness. This means that to one who is
devoted to the Supreme Lord Krishna or any of His authorised incarnations
the mind acts as a dear friend by His grace; but for all others the mind is
like an enemy. In the end of the verse it is indicated that the Supreme
Being aides within such a person.

Sri Vaisnava Sampradaya:

Ramanuja

Ramanuja's Commentary

The mind is only a friend to those who are able to restrain it from flowing
externally outwards after sense objects; but if one is unable to subdue the
mind that it will harass and aggravate one to satisfy the senses and is the
worst enemy. Lord Krishna is conveying that an ungoverned and uncontrolled
mind being attached to sense gratification interposes obstructions and
deviations in the way which deviates and hinders one from attainment of
atma tatva or realisation of the soul. Sage Parasara the father of
Vedavyasa has stated that the mind itself is the sole cause of bondage in
the material existence as well as the sole cause of moksa or liberation
from the material existence. A mind infatuated with desire for sense
objects constitutes a state of bondage and a mind free from the delusion of
desire for sense objects constitutes the way to moksa. The preliminary
competency to be acquired before one commences meditation will be given in
the next verse.

Kumara Vaisnava Sampradaya:

Nimbaditya

Kesava Kasmiri's Commentary

Now a question may asked as to whom is the mind a friend and for whom is
the mind an enemy? Lord Krishna clarifies that the mind is the friend to
that person who having complete control over the physical body, the senses
and the mind has conquered their lower nature. The mind is the enemy to the
person who is unable to control the physical body, the senses and the mind
due to not having conquered their lower nature. As is stated by the sage
Parasara: Man's mentality is verily the root cause of either their
liberation or their bondage. The mind obsessed with sensual pleasures is
bondage whereas the mind devoid of the desire to enjoy sensual pleasures
leads to moksa or liberation from material existence.